Ok...I was merely checking your syntax, not actually running the code. I'm not at my dev box, but here is why i think it is not compiling. When you read the column data out from the data row, use the tostring() method to convert it to a string.

Code:
foreach (DataRow dr in Tables.Rows) {
    TreView.Nodes.Add (new TreeNode(dr["TABLE_NAME"].ToString()));
}